Usually an HB (Horizontal Bridgiman) method and an LEC (Liquid Encapsulated Czochralski) method are well known as a method of producing a bulk crystal. However, an AlGaN single crystal is hardly grown by these methods.
Therefore, recently an attempt of the bulk crystal growth is made by a sublimation method and solution growth at high temperature and high-pressure. However, the AlGaN crystal which can be used for large-size substrate crystal is not obtained yet even by such methods.
Currently, hetero-epitaxial growth of AlGaN on a substrate (for example, sapphire substrate) by an HVPE (Hydride Vapor Phase Epitaxy) method is one of the most promising methods of producing the AlGaN single-crystal substrate. In the method, an Al source gas, a Ga source gas, and an NH3 source gas are mixed in a mixing portion, and the mixed gas is transported to a growth portion (also called substrate portion because the substrate is located). Then, AlGaN is grown on the sapphire substrate accommodated in the growth portion.
HVPE Method
Particularly a high growth rate is one of advantages in the HVPE method which is of a quartz reaction tube hot-wall method. Therefore, conventionally the HVPE method is used to produce a high sensitive photo-sensor in which a thick film is required and a power device (particularly, power-supply device in which GaAs is used) in which a thick-film, high-quality crystal is required, and HVPE method is also utilized as a method of producing the substrate, particularly a GaN substrate.
For example, Patent Document 1 “Gallium nitride based compound semiconductor crystal growth method (TOYODA GOSEI CO., LTD et al.)” and Patent Document 2 “Epitaxial wafer and production method thereof (Sumitomo Electric Industries, Ltd)” disclose that the HVPE method is utilized for the method of producing the GaN substrate.
The inventor developed a technique of producing a substrate made of a III-V compound including Al by HVPE (method), and the inventor made another patent application (Japanese Patent Application No. 2002-106102) (Patent Document 3).
Patent Document 1: Japanese Patent Laid-Open No. 10-215000
Patent Document 2: Japanese Patent Laid-Open No. 10-316498
Patent Document 3: Japanese Patent Laid-Open No. 2003-303774